Brake means for electric motors

ABSTRACT

A brake means for electric motors to stop rotation of the drive shaft immediately when the motor is de-energized. The motor shaft frictionally carries a brake plate and the brake plate bears frictionally against a surface of the rotor. The brake plate carries a stop-lug which is engageable by means of a solenoid operated plunger to stop the brake plate abruptly whereupon the rotor assembly is stopped frictionally. The plunger is actuated when the motor is de-energized and is retracted when the motor is energized.

v United States Patent [151 3,659,686 Markley 1 May 2, 1972 541 BRAKEMEANS FOR ELECTRIC 2,351,997 6/1944 Morill ..192/2 MOTORS 2,949,9898/1960 Lindstrom et al... .....l88/l71 X 3,169,607 2/1965 Romney..l88/171 X [72] lnventor: Joseph M. Markley, Southtngton, Conn.

- z 1d Primary Examiner-Duane A. Reger [73] Asslgnee Robbins Myers IncSpnngfie Attorney-Melville, Strasser, Foster & Hoffman [22] Filed: Jan.19, 1970 211 Appl. No.1 3,676 [57] ABSTRACT A brake means for electricmotors to stop rotation of the drive shaft immediately when the motor isde-energized. The motor g' g z dg shaft frictionally carries a brakeplate and the brake plate Fieid 7| 5 bears frictionally against asurface of the rotor. The brake i i 53 plate carries a stop-lug which isengageable by means of a sole. noid operated plunger to stop the brakeplate abruptly whereupon the rotor assembly is stopped frictionally. The[56] Re'erences Cited plunger is actuated when the motor is de-energizedand is UNITED STATES PATENTS retracted when the motor is energized.

1,162,370 11/1915 Keefer ..l88ll7l 3Claims,3DrawingFigures BRAKE MEANSFOR ELECTRIC MOTORS BRIEF SUMMARY OF THE INVENTION The invention relatesto a device for stopping an electric motor when its power is turned off,and more particularly to electro-mechanical brake means capable ofalmost instantly stopping rotation of the rotor under such conditions.

There are many types of equipment in which electric motors are used andwhich motors run intermittently and must be stopped within about onerevolution of the rotor. An example of such devices is a vending machinewherein the motor must accurately position an element and must thereforebe brought to a substantially immediate stop.

Because of the high speeds at which such motors run and the vast numberof stops and starts which they make under normal operating conditions,such brake means in use up to the present time have been a constantsource of trouble and have required frequent service or replacement.

According to the present invention, a brake means is provided whichoperates concurrently with de-energization of the motor and which is ofextremely simple construction so that it can operate indefinitely withlittle or no maintenance or repair.

Basically, the invention comprises a rugged stop member which is movedinto engagement with a stop on a brake plate frictionally mounted on themotor shaft such that the brake plate is abruptly and immediatelystopped. The brake plate is in frictional engagement with a surface ofequal area such as the end of the rotor which is rigidly mounted on themotor shaft. A friction disc may be interposed between the brake plateand the surface of the rotor. In this way the impact of the brake plateagainst the fixed stop member is rapidly dissipated by slippage betweenthe brake plate and the parts with which it is in frictional engagement.

The arrangement to be described hereinafter presents a number ofadvantages over prior motor braking systems. For one thing, aconsiderably larger area of frictional engagement between the brakingmember and the rotating member is provided. Additionally, the frictionsurfaces are not moved into and out of engagement with each other uponapplication or release of the brake but, on the contrary, they are inengagement with each other at all times and rotate together as a unitexcept during the very brief period of slippage when the motor isstopped. Means are provided for adjusting the braking surfaces so as topermit control of the amount of rotation of the shaft after the motor isde-energized.

The construction shown is of such nature that it can be mounted as aunit on standard motors with little or no modification of the motor. Itrequires a minimum of space so that the motor is not made excessivelybulky because of the braking device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary verticallongitudinal section through one end of an electric motor with thebraking device of the present invention attached thereto and with therotor of the motor shown somewhat diagrammatically and broken away;

FIG. 2 is a fragmentary vertical section taken on the line 2- 2 of FIG.1 and showing the brake plate of the braking device; and

FIG. 3 is a fragmentary horizontal section taken on the line 3-3 of FIG.1 showing the brake plate and the stop member engaging a stop-lug on thebrake plate.

DETAILED DESCRIPTION With reference to FIG. 1, only the rotor 10, driveshaft 12 and end-plate 14 of a conventional electric motor are shown.Other parts of the motor including the housing and windings whichsurround the rotor, as well as the front or driving end of the motor,have been omitted for purposes of clarity. The rotor assembly includingthe drive shaft 12, to which the rotor 10 is rigidly fixed, is mountedin suitable bearings at both ends of the motor for substantiallyfrictionless rotation. Oneof the ball bearings 16 for shaft 12 is'shownin FIG. 1 in the rear endplate 14 of the motor. Power is suppliedfordriving the motor 'by apair of leads l8, 19, connected at terminals20 and 21, respectively, of a terminal block 22, from which suitableconnections (not shown are made to the motor coil.

Mounted on a'bracket 23 on the outside of the end-plate 14 is anactuating solenoid 24, whichhas its core 26 extending upwardly andparallel to the plane of the end-plate 14. The uppertend of core 26 isslotted lengthwise for connection with a bell-crank 28 which is pivotedto the end-plate 14 on a rocker pin 30. The rocker pin 30 is supportedon ears 32 which are bent outwardly from the upper mounting leg23a ofthe bracket 23.

A bell-crank 28 which may be of sheet metal, fits within the slotted endof the core 26. A horizontal slot 34 is provided in the edge of theportion of the bell-crank 28 which fits within the slotted end ofsolenoid core 26, and a pin 36 through the end of the core 26 rides inthe slot 34. In this manner the bellcrank 28 is pivoted back and forthupon vertical movement of the core 26.

In the embodiment here shown, the core 26 is constantly urged upward bya coil spring 38 in order to pivot the bellcrank 28 in a clockwisedirection. When power to the motor is supplied through the leads l8, 19,the solenoid 24 is energized through the leads 40, 41 connected to thesolenoid coil and to the main terminals 20, 21 on the terminal block 22.Energization of the solenoid 24 draws the core 26 downward against theeffort of the coil spring 38, thereby pivoting the bell-crank 28 in acounterclockwise direction. The coil spring 38 is held in compressionbetween the upper end of the coil of the solenoid 24 and a washer 42,which is retained by a split ring 44 in a peripheral slot in the core26.

A stop-plunger 46 is supported for longitudinal movement in a bushing48, extending through the end-plate 14 of the motor, and the outer endof the plunger 46 is connected to the bell-crank 28 by a pin 50. The endof the stop-plunger 46, through which the pin 50 passes, is slotted toreceive the bellcrank 28, and the pin 50 rides in a vertical slot 52 inthe bellcrank in the same manner that the solenoid core 26 is connectedthereto. Thus, as the solenoid 24 is energized and deenergized, drivingits core 26 up and down, the movement of the core 26 is transferred tothe stop-plunger 46 to move its inner end 54 into and out of the path ofa rearwardly projecting stop-lug 56 which is rigidly mounted adjacentthe periphery of a brake plate 58 at the rear end of the rotor 10 of themotor. The brake plate 58 is mounted frictionally on the shaft 12 sothat it normally rotates with the rotor 10.

As may be seen in FIG. 2, brake plate 58 is provided in this instancewith two stop-lugs 56, which are diametrically opposed to each other onthe brake plate and project rearwardly therefrom. The brake plate 58 ismounted on the motor shaft 12 for frictional engagement along its entirefront face with a fiber disc 60, the opposite side of which abuts thecircular rear end surface of the rotor 10. Both brake plate 58 and disc60 are circular and supported at their centers on an outer, flangedbushing 62 and an inner liner 64 having a slip fit on the motor shaft12. The liner 64 may be made of nylon or some other tough bearingmaterial and desirably is provided with inner and outer flanges betweenwhich the bushing 62 is held. A lock-nut 66 is threaded onto the shaft12 outward of the brake plate 58, and a spring washer 68 and a fiatmetal washer 70 are placed in that order on the shaft 12 between brakeplate 58 and the lock-nut 66. As the lock-nut 66 is tightened down onthe shaft 12, the spring washer 68 is compressed, thereby exerting thedesired pressure between the faces of brake plate 58 and fiber disc 60.

It will be apparent from the foregoing description that when the motoris energized, the solenoid 24 is also energized, so that thestop-plunger 46 is withdrawn from the path of the stop-lugs 56 on thebrake plate 58. When the power to the motor is disconnected by controlmeans (not shown), the solenoid 24 is de-energized, permitting its core26 to be moved upward by the coil spring 38 in order to pivot thebell-crank 28 clockwise. This in turn drives the stop-plunger 46 inward,so that its inner end 54 moves into the path of the revolving stoplugs56 on the brake plate 58. One of the lugs 56 therefore immediatelystrikes the end 54 of the stop-plunger 46 causing the brake plate 58 tocome to a sudden stop. Rotation of the rotor and shaft 12 are thenlikewise brought to a rapid stop because of the frictional engagementbetween the brake plate 58, fiber disc 60 and rotor 10. The amount ofrotation which the rotor 10 will make after the brake plate 58 isstopped will depend in part on the amount of pressure exerted by thebrake plate 58 against the fiber disc 60 and the end-surface of therotor 10. I

In order to ensure that the stop-plunger 46 can not become jammed inengagement with the stop-lug 56 when the motor is restarted, so that thesolenoid 24 would be unable to retract the plunger 46, the end 54 of theplunger 46 is cut at an angle on both sides, as shown in FIG. 3. Inpractice, it has been found that flats cut at 5 to the longitudinal axisof the plunger 46 will prevent the plunger from becoming hung up on thestop-lug 56 as the motor starts. If desired a single stop-lug 56 maysuit the purpose in place of the two shown, or for that matter, anynumber of such stop-lugs may be provided on the brake plate 58.Furthermore, notches or other suitable stop surfaces may be provided onthe brake plate in place of the stop-lugs 56.

Referring to the manner in which the solenoid 24 is mounted on themotor, it will be apparent that in situations where space permits, thesolenoid may be mounted perpendicular to the end-plate 14 of the motor,in which case the core of the solenoid would be extended so that itcould move directly into engagement with the brake plate 58; and in suchcase the bell-crank 28 and stop-plunger 46 could be eliminated. In mostcases, however, this would make the solenoid project too far to the rearof the motor and would be objectionable for that reason.

The mounting bracket 23 for the solenoid 24 is desirably fastened to theend-plate 14 of the motor at its upper end by the head 48a of a guidebushing 48, which fits within an openended slot in the upper leg 23a ofthe bracket 23 and is threaded into the end-plate 14 of the motor asshown. The lower leg 23b of the bracket 23 is secured to the end-plate14 by a screw 72. The entire assembly can therefore be readily installedor removed as a unit, by simply loosening the bushing 48 and removingthe mounting screw 72.

It will be understood by those skilled in the art that various changesand modifications can be made inthe specific device herein described andshown in the drawings without departing from the scope of the inventionas defined in the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. in an electric motor having a frame and a rotor assembly including adrive shaft rotatingly mounted on said frame, a braking device forpositively and rapidly stopping rotation of the drive shaft when saidmotor is deenergized, comprising in combination:

a. a brake plate comprising a circular disc frictionally mounted at itscenter on said rotor assembly for rotation with said drive shaft,

b. a stop-lug fixed on said brake plate adjacent the periphery thereof,said stop-lug moving in a rotary path when said brake plate rotates,

c. a stop member comprising a plunger slidably mounted on said motorframe for longitudinal movement axially of said motor drive shaft intothe path of said lug, for positively arresting rotation of said brakeplate,

d. said plunger being mounted the same distance radially of said driveshaft as said stop-lug, and

e. actuating means for moving said stop member into engagement with saidface of the circular disc for engagement by said stop-lug uponde-energization of said motor in order to stop said brake plate androtor assembly, and

for moving it out of the path of said stop-lu upon energization 0 saidmotor to permit rotation 0 said brake plate and rotor assembly, saidfrictional mounting serving to dissipate the impact of said stop-lug onsaid brake plate to said rotor assembly.

2. A braking device as set forth in claim 1, which includes a secondstop-lug fixed on said face of said circular disc diametrically oppositesaid first stop-lug and equidistant from the axis of rotation thereof.

3. A braking device as set forth in claim 1, wherein said rotor assemblyis provided with a circular end surface, and a fiber disc is mountedcoaxially with said brake plate on said motor drive shaft insurface-to-surface engagement with said brake plate, and between saidbrake plate and circular end surface, and a lock-nut threaded onto saiddrive shaft adjacent said brake plate on the opposite side thereof fromsaid fiber disc, and a spring washer disposed between said lock-nut andbrake plate to urge said brake plate axially into engagement with saidfiber disc, and for increasing the pressure between said brake plate andfiber disc as said lock-nut is tightened against said spring washer.

1. In an electric motor having a frame and a rotor assembly including adrive shaft rotatingly mounted on said frame, a braking device forpositively and rapidly stopping rotation of the drive shaft when saidmotor is de-energized, comprising in combination: a. a brake platecomprising a circular disc frictionally mounted at its center on saidrotor assembly for rotation with said drive shaft, b. a stop-lug fixedon said brake plate adjacent the periphery thereof, said stop-lug movingin a rotary path when said brake plate rotates, c. a stop membercomprising a plunger slidably mounted on said motor frame forlongitudinal movement axially of said motor drive shaft into the path ofsaid lug, for positively arresting rotation of said brake plate, d. saidplunger being mounted the same distance radially of said drive shaft assaid stop-lug, and e. actuating means for moving said stop member intoengagement with said face of the circular disc for engagement by saidstop-lug upon de-energization of said motor in order to stop said brakeplate and rotor assembly, and for moving it out of the path of saidstop-lug upon energization of said motor to permit rotation of saidbrake plate and rotor assembly, said frictional mounting serving todissipate the impact of said stop-lug on said brake plate to said rotorassembly.
 2. A braking device as set forth in claim 1, which includes asecond stop-lug fixed on said face of said circular disc diametricallyopposite said first stop-lug and equidistant from the axis of rotationthereof.
 3. A braking device as set forth in claim 1, wherein said rotorassembly is provided with a circular end surface, and a fiber disc ismounted coaxially with said brake plate on said motor drive shaft insurface-to-surface engagement with said brake plate, and between saidbrake plate and circular end surface, and a lock-nut threaded onto saiddrive shaft adjacent said brake plate on the opposite side thereof fromsaid fiber disc, and a spring washer disposed between said lock-nut andbrake plate to urge said brake plate axially into engagement with saidfiber disc, and for increasing the pressure between said brake plate andfiber disc as said lock-nut is tightened against said spring washer.